The present invention relates to a process window seal that will transmit microwave energy and includes a surrounding ring with seals to reduce or prevent microwave energy leakage. The ring contains the window seal to avoid creep or cold flow across a wide range of temperatures to avoid failures under operating pressures.
In the past, there have been considerable developments in the use of microwave (radar) gauges for determining tank levels. These gauges depend upon transmitting microwave energy toward a surface of material inside a tank or container, and then receiving an echo or return signal to determine the level of the material sending the echo. The correct type of device depends in part on the overall distance that needs to be measured, that is the height of the material in the tank between its lowest level and its highest level. Also, the surface conditions of the materials are of importance in measuring tank level, as are the dielectric constant or conductivity of the material to be measured.
In using a radar gauge, the process tank or container that is to be monitored can sometimes be at a very high temperature, as well as at a high pressure. In such instances, it is necessary to have a pressure containing window seal between the radar instrument and the interior of the tank, to protect the instrument from harsh, corrosive process materials. The window seal has to be able to transmit microwave energy for operation of the radar gauge.
Various manufacturers have advanced radar gauges, including the MICROPILOT radar gauge made and sold by Endress+Hauser. These devices are used for determining levels of various materials.
Window seals made of polytetrafluoroethylene (PTFE) are commonly used, but under high temperatures and high pressures they will tend to flow, so that the pressure carrying capability is reduced at such high temperatures. Usually the need for high pressure performance is when the temperature is high as well. Thus, being able to control the flowing of the PTFE at process temperatures is desirable for maximum utilization of the window materials.